Prediction of turbulent flow structure in a fully developed rib-roughened narrow rectangular channel

Abstract

Fully developed turbulent water-flow structure over one-side repeated-ribs in narrow two-dimensional rectangular channels was investigated experimentally by Particle Image Velocimetry (PIV) and analytically by the standard κ−ε and nonlinear κ−ε turbulent models. Two rib-pitch to height ratios (p/k) of 10 and 20 were investigated while the rib height was held constant at 4 mm. The rib height-to-channel equivalent diameter ratio (k/De) was 0.1. The streamwise mean velocity and turbulent kinetic energy distributions at six selected axial stations from the center rib for the two Reynolds number (Re) of 7,000 and 20,000 were obtained and compared with the predicted one.The performance ability in predicting separating and reattaching turbulent water-flow between the standard κ−ε and nonlinear κ−ε models had yielded no clear conclusion. A large-scale turbulent eddy was generated by the rib promoter and then propagated into the mainstream flow, which led to the deformation of the velocity profile. The turbulent kinetic energy was increased about two times higher at p/k = 20 than that at p/k =10 under the two Reynolds numbers. The effect of the p/k value and the Reynolds number (Re) on reattachment length (XR) was investigated and showed that the p/k and Re had no significant effect on the reattachment length beyond a critical value of Re = 15,000 where XR was found to be approximately 4 times of the rib height under water-flow condition.

Turbulent couette flow between corrugated walls: The case with motion of one wall perpendicular to the corrugation cavities

“…The equations of motion were solved numerically using a commercially available CFD package, FLUENT, using a second order accurate finite volume method with a realizable model as the closure equations for turbulence. There is some indication in the literature that this turbulence model should be adequate for our purposes as both Mesalhy et al and Shafiqul et al have used this for driven cavity flow. For all cases, the flow domain was discretized using a non‐uniform structured mesh (see Figure ).…”

“…A number of authors have examined the local flow field within the roughness elements either by direct flow visualization or through computation . With flow over square‐ribbed roughness elements, phenomenologically characterized two distinct flow fields, that is, d ‐ or k ‐type.…”

Calibration of κ-ε turbulence model for thermal–hydraulic analyses in rib-roughened narrow rectangular channels using genetic algorithm

“…Islam et al [3] conducted a similar study on rectangular narrow channels with square microribs. He later extended the work to analyze the influence of turbulence flow structure on the enhancement of heat transfer in those channels [4,5]. Chang, Liou and Lu [6] studied heat transfer enhancement in narrow rectangular channel with two opposite rib-roughened walls.…”

“…The stream-wise mean velocity and turbulent kinetic energy distributions at different locations for the Re = 7,000 and 20,000 were obtained. The values were also compared with the predicted values by the standard κ-ɛ and nonlinear κ-ɛ turbulent models [5]. Results revealed that both the turbulence models failed to predict accurately the flow characteristics over the rib-roughened surface.…”